Characterization and expression of chalcone synthase in different genotypes of Matthiola incana R.Br. during flower development

Anthocyanin regulatory and structural genes associated with violet flower color of Matthiola incana

MAIN CONCLUSION

MiMYB1 and MibHLH2 play key roles in anthocyanin biosynthesis in Matthiola incana flowers. We established a transient expression system using Turnip mosaic virus vector in M. incana. Garden stock (Matthiola incana (L.) R. Br.) is a popular flowering plant observed from winter to spring in Japan. Here we observed that anthocyanin accumulation in 'Vintage Lavender' increased with flower development, whereas flavonol accumulation remained constant throughout flower development. We obtained five transcription factor genes, MiMYB1, MibHLH1, MibHLH2, MiWDR1, and MiWDR2, from M. incana floral cDNA contigs. Yeast two-hybrid analyses revealed that MiMYB1 interacted with MibHLH1, MibHLH2, and MiWDR1, but MiWDR2 did not interact with any transcription factor. Expression levels of MiMYB1 and MibHLH2 increased in petals during floral bud development. Their expression profiles correlated well with the temporal profiles of MiF3'H, MiDFR, MiANS, and Mi3GT transcripts and anthocyanin accumulation profile. On the other hand, MibHLH1 was expressed weakly in all organs of 'Vintage Lavender'. However, high expression levels of MibHLH1 were detected in petals of other cultivars with higher levels of anthocyanin accumulation than 'Vintage Lavender'. MiWDR1 and MiWDR2 maintained constant expression levels in petals during flower development and vegetative organs. Transient MiMYB1 expression in 1-month-old M. incana seedlings using a Turnip mosaic virus vector activated transcription of the endogenous anthocyanin biosynthetic genes MiF3'H, MiDFR, and MiANS and induced ectopic anthocyanin accumulation in leaves. Therefore, MiMYB1 possibly interacts with MibHLH2 and MiWDR1, and this trimeric protein complex activates the transcription of anthocyanin biosynthetic genes in M. incana flowers. Moreover, MibHLH1 acts as an enhancer of anthocyanin biosynthesis with the MiMYB1-MibHLH2-MiWDR1 complex. This study revealed the molecular mechanism involved in the regulation of anthocyanin accumulation levels in M. incana flowers.

Exogenous gibberellic acid reprograms soybean to higher growth and salt stress tolerance

The agricultural industry is severely affected by salinity due to its high magnitude of adverse impacts and worldwide distribution. We observed the role of exogenous gibberellic acid (GA(3)) in salinity alleviation of soybean. We found that GA(3) application significantly promoted plant length and plant fresh/dry biomass while markedly hindered by NaCl induced salt stress. The adverse effect of salt stress was mitigated by GA(3), as growth attributes significantly recovered, when GA(3) was added to salt stressed soybean plants. Elevated GA(3) treatments increased daidzein and genistein contents (commonly known as phytoestrogens) of soybean leaves under control and salt stress conditions. Phytohormonal analysis of soybean showed that the level of bioactive gibberellins (GA(1) and GA(4)) and jasmonic acid increased in GA(3) treated plants, while the endogenous abscisic acid and salicylic acid contents declined under the same treatment. GA(3) mitigated the adverse effects of salt stress by regulating the level of phytohormones, thus aiding the plant in resuming its normal growth and development. The presence of GA(1) and GA(4) showed that both early-C13-hydroxylation and non-C13-hydroxylation pathways of GA biosynthesis are functional in soybean. It was concluded that GA(3) ameliorates the adverse effects of salt stress and restores normal growth and development of soybean.

Characterization and structural features of a chalcone synthase mutation in a white-flowering line of Matthiola incana R. Br. (Brassicaceae)

For Matthiola incana (Brassicaceae), used as a model system to study biochemical and genetical aspects of anthocyanin biosynthesis, several nearly isogenic colored wild type lines and white-flowering mutant lines are available, each with a specific defect in the genes responsible for anthocyanin production (genes e, f, and g). For gene f supposed to code for chalcone synthase (CHS; EC 2.3.1.74), the key enzyme of the flavonoid/anthocyanin biosynthesis pathway belonging to the group of type III polyketide synthases (PKS), the wild type genomic sequence of M. incana line 04 was determined in comparison to the white-flowering CHS mutant line 18. The type of mutation in the chs gene was characterized as a single nucleotide substitution in a triplet AGG coding for an evolutionary conserved arginine into AGT coding for serine (R72S). Northern blots and RT-PCR demonstrated that the mutated gene is expressed in flower petals. Heterologous expression of the wild type and mutated CHS cDNA in E. Scherichia coli, verified by Western blotting and enzyme assays with various starter molecules, revealed that the mutant protein had no detectable activity, indicating that the strictly conserved arginine residue is essential for the enzymatic reaction. This mutation, which previously was not detected by mutagenic screening, is discussed in the light of structural and functional information on alfalfa CHS and related type III PKS enzymes.

The chalcone synthase multigene family of Petunia hybrida (V30): differential, light-regulated expression during flower development and UV light induction

We have analysed the expression of the 8-10 members of the gene family encoding the flavonoid biosynthetic enzyme chalcone synthase (CHS) from Petunia hybrida. During normal plant development only two members of the gene family (CHS-A and CHS-J) are expressed. Their expression is restricted to floral tissues mainly. About 90% of the total CHS mRNA pool is transcribed from CHS-A, wheares CHS-J delivers about 10% in flower corolla, tube and anthers. Expression of CHS-A and CHS-J during flower development is coordinated and (red) light-dependent. In young seedlings and cell suspension cultures expression of CHS-A and CHS-J can be induced with UV light. In addition to CHS-A and CHS-J, expression of another two CHS genes (CHS-B and CHS-G) is induced in young seedlings by UV light, albeit at a low level. In contrast to CHS genes from Leguminoseae, Petunia CHS genes are not inducible by phytopathogen-derived elicitors. Expression of CHS-A and CHS-J is reduced to a similar extent in a regulatory CHS mutant, Petunia hybrida Red Star, suggesting that both genes are regulated by the same trans-acting factors. Comparison of the promoter sequences of CHS-A and CHS-J reveals some striking homologies, which might represent cis-acting regulatory sequences.

Purification and characterization of (+)dihydroflavonol (3-hydroxyflavanone) 4-reductase from flowers of Dahlia variabilis

Individual flowers from inflorescences of Dahlia variabilis (cv Scarlet Star) in young developmental stages contained relatively high activity of (+)-dihydroflavonol (DHF) 4-reductase. The DHF reductase was purified from such flowers to apparent homogeneity by a five-step procedure. This included affinity adsorption on Blue Sepharose and elution of the enzyme with NADP+. By gel filtration and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis it was shown that DHF reductase contains only one polypeptide chain with a Mr of about 41,000. The reductase required NADPH as cofactor and catalyzed transfer of the pro-S hydrogen of NADPH to the substrate. Flavanones and dihydroflavonols (3-hydroxyflavanones) were substrates for DHF reductase with pH optima of about 6.0 for flavanones and of about 6.8 for dihydroflavonols. Flavanones were reduced to the corresponding flavan-4-ols and (+)-dihydroflavonols to flavan-3,4-cis-diols. Apparent Michaelis constants determined for (2S)-naringenin, (2S)-eriodicytol, (+)-dihydrokaempferol, (+)-dihydroquercetin, and NADPH were, respectively, 2.3, 2, 10, 15, and 42 microM. V/Km values were higher for dihydroflavonols than for flavanones. Conversion of dihydromyricetin to leucodelphinidin was also catalyzed by the enzyme at a low rate, whereas flavones and flavonols were not accepted as substrates. DHF reductase was not inhibited by metal chelators.

Isolation and characterization of buckwheat (Fagopyrum esculentum M.) chalcone synthase and its polyclonal antibodies

Chalcone synthase was isolated from illuminated buckwheat (Fagopyrum esculentum M.) hypocotyls and purified to electrophoretic homogeneity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis using (NH)4SO4 fractionation, gel filtration on AcA 44, ion exchange chromatography on DEAE-Bio-Gel, and HPLC on hydroxylapatite. The properties of the enzyme were pH optimum, 8.0; Mr approximately 83,000 +/- 1000; Mr subunit, approximately 41,500 +/- 500; isoelectric point, pH 5.2; Km, 1 X 10(-6)M for malonyl-CoA, and 0.6 X 10(-6) M for p-coumaryl-CoA. Buckwheat chalcone synthase used p-coumaryl-CoA as substrate and also utilized caffeyl-CoA and ferulyl-CoA at 20 and 80%, respectively, of the rate of p-coumaryl-CoA in the chalcone synthase reaction. Antibodies against the buckwheat chalcone synthase were developed in a New Zealand white rabbit and characterized for specificity by enzyme-linked immunosorbent assay, Ouchterlony double immunodiffusion, and Western blotting.

Enzymatic control of anthocyanin expression in the flowers of pea (Pisum sativum) mutants

Using enzymological and immunological methods we have investigated the relationship between chalcone synthase and the A locus, a major gene involved in the control of anthocyanin expression in pea (Pisum sativum L.) flowers. Pea plants containing the dominant allele A usually synthesize anthocyanins in the petal tissue, whereas plants homozygous for the a allele do not produce anthocyanins. We sought to determine whether or not the A locus also controlled the presence or absence of chalcone synthase, the first enzyme of the flavonoid pathway in the flowers of three genetic lines (A, purple-violet flowers; A,am, white flowers with sometimes pink edges; and a, white flowers). Chalcone synthase was found to be present in all three genetic lines by enzyme activity measurement, indirect enzyme-linked immunosorbent assay (ELISA), and Western blotting. Spectroscopic investigations showed that only the genetic lines A and A,am contained anthocyanins and flavonol glycosides, respectively, in the flowers; line a accumulated p-coumaric acid or its derivatives. These data suggest that the A locus in Pisum is not the structural gene for chalcone synthase and it does not appear to regulate the expression of this enzyme.